Electrical measuring instrument.



E. F. NORTHRUP.

ELECTRICAL MEASURING INSTRUMENT.

APPLICATION FILED DBO. 7, 1908.

Patented Mar. 1, 1910.

M 6 M W 3 V 1) areas TEMP.

Inz/entor' Witnesses UNITED STATES PATENT OFFICE.

EDWIN F. NORTHRUP, OF PHILADELPHIA, PENNSYLVANIA, AS SIGNOR T LEEDS AND NORTHRUP COMPANY, A. CORPORATION OF PENNSYLVANIA.

ELECTRICAL MEASURING INSTRUMENT.

To all whom it-may concern:

Be it known that I, EDWIN F. NoR'rHRUP,

a citizen of the United States, residing in the city of Philadelphia, county of Philadelphia, and Stateof Pennsylvania, have invented a certain new anduseful Electrical Measuring Instrument, of which the following is v,.a specification. v My' invention relates to an electrical .0 measuring instrument, preferably direct reading, involving the use of a differential ,galvanometer, as of the DArsonval, moving magnet, or other type, or involving the use of a differential telephone, for electrically 1 5 measuring temperatures as, for example, in the case where a resistance is employed for temperature measurement, such resistance changingwith temperature; or.for making electrical measurements other than those relating to temperature.

In one -of 1ts forms my invention resides in acircuit-"or resistance balancing device, in which the coils of a'difi'erential galvanomj eter, differential telephone, or other differential device, are connected in different circuits or branches',and a slide wire or adjustable resistance constitutes balancing means, a direct reading scale, preferably uniform, being provided for reading directly in temperature units, or other units; and it is a further feature of my invention, in such arrangement, to provide a shunt for the slide wire or adjustable resistance so as to change the extent of the range of the instrumen't; and it is a further feature of my. invention to provide in one of the circuits or branches a-suitable resistance for shifting the scale range of the instrument, as will,- be hereinafter explained. And it is a further feature of my invention to employ for the slide :wire or adjustable'resistance a conductor whose resistance does not increase uniformly with its length, but is modified so as to increase non-uniforml and in a manner to correct for the variation from a straight line or linear function of any variation of resistance or other property of any element connected in one or more circults or any associated circuit.

A further feature of my invention resides in the employment of ,onlythree thermometer leads, in the case of electrical temperature measurement, and arranged and combranches of the balancing arrangement, or in l nently connected in shunt to bined, with other elements as to perfectlyv I Specification of Letters Patent. Patented Mar, 1, 1910, Application filed December 7, 1908. Serial No. 466,242.

eliminate all error which in other arrangements is introduced when only three ther- 1 had'to the accompanying drawing, in which g F igure 1 is a diagrammatic View of a circu1t or resistance balancingdevice adapted ture in accordance with an illustrative of my invention. Fig. 2 is a fragmentary view illustrating a form the slide wire or adjustable resistance may take. Fig. 3 is a cross for the electrical measurement of temperasectional view through a resistance of the type shown in Fig.1 2, but on a'line as Z-Z, Fig 2, showing non-uniform or modified cross section for securing non-uniform or modified resistance. Fig. 4 illustrates a graphic method of determining to what extent and in what manner to modify or vary the slide wire or adjustable resistance. y

In Fig. l, the circuit or resistance balancin arrangement comprises the slide wire or ad]ustable resistance conductor V extending between the points a. and b, and engaging .with the conductor W is the movable-or sliding contact 10. The portions of the resistance conductor W to the right and left of the sliding contact -w constitute variable resistances indifferent circuits or branches; one of" these branches extends through G and T to the point d, one terminal of the resistance. T which may be an unknown resistance. to be measured or'any other resistance, and in electric thermometry is the bulb or thermometer resistance. I Another branch of" the resistance balancing device extends through G and R 'to the point cl. And between the point d and the sliding contact ware connected the source of energy B and a resistance r. And in shunt to the slide wire or adjustable resistanceW may be connected a shunt resistance S by the closure It is to be understood, however, that the shunt S may be either presentor absent, according to circumstances hereinafter described, and when present ma be permaintervention of a plug or switch.

without the V The sliding contact to is adapted to carry a pointer which cooperates with or moves over the two uniformly graduated scales 6 and f. i

G and G are the coils or windings of' a differential galvanometer, such as a DArsonval galvanometer, or a galvanometer of .the moving magnet type, or any other ings so connected in circuit that the torque,

due to the coil G exactly nullifies or balances the torque due to the coil G when the same amount of current is flowin throu h each. And, in such case, the coils and being bifilarly wound, the two coil conductors may bewound into a coil side by side as if a single conductor, so as to insure that the windin 'G shall be subjected to exactly the same'fie d as the winding G. 7 Furthermore, the resistance of G shall be equal to the resistance of .G, and the number of turns in the coil G shall equal the number of turns in the coil G.

, uring instrument. In other words, the ther-- While, as above stated, the resistance T maybe any known or unknown resistance of any character and for any urpose, it will be here described as the bu b or thermometer resistance such as used in electrical temperature measurements. In such case the resistance T may be a platinum, nickel, or

other suitable wire or conductor, inclosed in a suitable envelop or bulb, and havin a definite temperature coefiicient and a 'de inite initial resistance. That is to say, .the thermometer is preferabl an, interchangeable one; that is, once any" number, all having the same .temperature'coeflicient and all having the same resistance atordinarytemperatures. I I,

a y and y' are the thermometer leads which extend from the terminals of the resistance T to the binding posts A and B of the measmometers T may be at any distance from the instrument and there may be any number, interchangeable, as above stated, and means for. connecting any one of them to the instrument. There is included between the sliding .contact to and the bindin post C the source of energy B and the resistance r- This resistance r is provided preferably when the source B is an ordinary llghtlng or power circuit as, for example, a 1.10 volt circuit. If the source B be of far less potential the resistance 1' may be accordingly reduced in value or even entirely omitted.

From the binding post C to the terminald braid, so that bot-h are subjected to the same temperature conditions.

Calling L the entire resistance of the slide wire or resistance conductor W, and c the re-.

sistance of the conductor W between the rider or sliding contact 'w and the point a,

and remembering that the resistance of G is equal to the resistance of G, and'that and y are similar in resistance (being similar in material, len th, and cross. section) We have, for a con it-ion of balance *when the shunt S is not equation:

This means that the variation of the resist v ,1

ance T with respect to c, the amount of resistance between the point a and the sliding' contact w, is constant and that T varies present, the following But R is a con-' twice as fast as c. Therefore, the resistance i L, that is, the total resistance of the slide wire or adjustable resistance W is taken equal to one-half of the total resistance increment of the bulb resistance T"w'hen the shunt S is not present' Thus, assuming that the instrument is to'be used for measuring temperatures between certain limits and thatbetween those limits of temperature the resistance'T increases ten ohms, then the slide wire W need have a totalresistance'of only five ohms, though in practice it mi ht be given a somewhat larger resistance. t fol-' lows, therefore, that by taking the wire or.

conductor JV of more or less resistance thev the resistance T at the temperature t. And

for best sensibility of the instrument the resistance of each coil G and G is taken equal to R, that is, equal to the resistance T at the low end of the temperature iiiterval to .be measured.

The resistance of the bulb conductor T increases as the temperature to which it is subjected increases. 'But the law of variation of resistance with temperature is not a simple proportion or linear. function, except over small temperature variations. In consequence, the scale, as c, with which the pointer on the sliding contact w cooperates, will'not be a uniform one, i. ethe distances between different scale divisions will not all be equal to eachother. If, however, the nature of the resistance T is such that its variation from a linear function is very slight, the instrument scale may be made uniform as to its scale divisions. But since the law of variation of T'is not a linear function orv a simpleproportionfantl to still be able to use a uniform scale on the instrument, the slidla wire or resistance W must not increase in resistance uniformly with its length measured from the low tem--v perature end of the scale. That is to say, the wire or conductor W must not increase in resistance uniformly from point a toward point I), but must increase non-uniformly to correct for the non-uniform increase in resistance of T with increasing temperature.

Accordingly, assuming that the resistance of T does not increase as rapidly as the tempera'ture to which it is subjected, that is, assuming that the resistance temperature curve of T -1s represented by the curve h, Fig. 4, correction or modification in the wire W may be determined by the. methodnow to be described: f In Fig. "4 distance or abscissae measured along the horizontal axis O,X are temperatures above the lowest to which the ther- "mometer is subjected. For convenience of explanation this minimum temperature is called 0. Ordinates or distances measured along the axis OY represent increments in resistance in ohms of the bulb or thermometer resistance T. The resistance for convenience of explanatlon is called 0 at the minimum temperature. The curve 72, is determinedby sub ecting the resistance T to difl'e'rent temperatures, measuring each temperature by an air thermometer, or other means, and measuring the resistance of T foreach of such temperature falls short of the straight'line- 0-9 by anamount 2'; at 900 degrees byan amount-j; at, 800- degrees by an-amountm," at 700 degrees by an amount a, and soon.

The line 07-9 is now drawn at an angle with the'axis e 0 X such that theslope of or thermometer the sliding contact to, varies just one-half as rapidly as T. Then, at the 1,000 degree orslope of the line O'g. This for the reason that'the resistance 'of, between point a and .dinatea points is taken at a distance below gequal to one-half of 2'. And so on at the other ordinates, points are taken below the line Og equal to one-half of Lone-half of m, one-half of n, and soon. These points then determine the curve it drawn between 8- v Assuming now that the range of the instrument is from 500 to 1,000 degrees, auniform scale, 6, readingjfrom 500 to 1,000 degrees is placed upon the instrument. But the resistance of the conductor V is-so modified or varied thatatthe different positions of the pointer on w the resistances of W correspond. with the ordinates of the curve u at the respective temperatures. The sl ide Wire or conductor, 7 may then be decreased in itscross section, the cross section varying throughout its length so that at different scale positions of slider w.the' resistances of V measured from a to -10,

.that is, a, shall correspond with the ordi nates' of the'curve peratures.

lVhile the slide Wire or variable resistance W may be a straight wire ,over Whose entire u at the different tcin-.

length the contact wmay engage and whose cross section may be varied throughout its length, as. above'described, such conductor 7 may be dispdsed in a' helix, a fragmemtary port-ion of Which is shown in F 2.

' the insulated conductor 3 being bared, and

buffed or ground as at 4, according to prior Letters Patent of the United States No. 862,842, heretofore granted to me. Then,- to modify or taper the resistance of the conductor to correctfor the resistance T, the

conductorWV may be ground or buffed ofl' to a greater or less extent thronghoutiits length, as shown in Fig. 3, which is a longitudinal cross section on the line Z-Z of F ig.2, insulation-being omitted for clearness. It. is to be understood, however, that the variation in the cross section shown in Fig. 3 does not-necessarily corres 0nd to the corrections required as shown *moved along, the resistance 0, 0 .Fig. 1, .doesnot increase uniforml but increases in"such nianiier as to compensate for the -varlatlon' from 'a 1111881 law of the resistance y Fig. 4', but 'is illustrative only'of' how throughout Tandyet make it possiblefto use a uniform scale. Inthis way any number of "scales may be made and stamped at one time for any number of instruments.

-cuit by -plug ing or otherwise.

' \Vith a iven slide wire or adjustable resistance a given range of temperatures may be measured; To change the range of temperature n1easured, without inany Way changing the resistance of V, a shunt S may be brought into circuit by the closure of a switch or the insertion of'a plug, as p, or by permanently connectin the resistance S to, the points a and b. T is will reduce the scale range; of the instrument; or a sec ond scale, as f, may be provided in the case. where the shunt S may be brought into cir- That is, without the siunt S scale e may be used,- and when S is connected in circuit the second scale f is read. Or by making the instruments all alike or standard when the shunt S is present only a single scale 7' may be provided, which, however, is different from the scale e which would be if the shunt S were absent.

' With the shunt S in circuit as shown, and L being uniform, we have the equation:

2S and STE times as fast as T. Suppose S is infinite, that is, that S is absent, we then provided which agrees with equation (4) supra.

range of the instrument to be from 500 to 1,000 degrees with the shunt S absent, by j the use 'of suchshunt the range may be changed to 500 degrees to 600 degrees.

The proper resistance value to ive-the. slide wire or adjustable resistance ,is: S+'L- L 1110.0 2S inc. T (9) where iric.- c isthe total increment or in-' fixed resistance 'ment may be shifted as from 500 degrees to resistance value to give to S. This is determined by solving equation 9 for S, which 'ves: I g1 Linc.T

2L-inc. T

Increment T and L being known in any case, S is easily determined.

If inc. T=2L, S is infinite, and there should be no shunt resistance Thus, as a particular case, suppose that due to the increase in temperature from 500degrees to 1,000 degrees T increases 10: (ten ohms) in resistance. And suppose the slide wire has a resistance L fiw, then by substituting these values in equation 10, we find that S:30w. I I A shunt S may at all'tirnesbe used when it is true of the bulb or thermometer resistance, or other resistance T, that its resistance is a linear function of temperature or very nearly so. In the case where a tapered or modified slide wire or adjustable resistance W is used, as hereinbefore described, for the purpose of compensating or correcting for variations from'a linear function, a shunt S of relatively low resistance cannot be used, without introducing considerable error. However, when a tapered or modified slide Wire or adjustable resistance W is used, a

shunt S ofrelatively high resistance may be employed with the introduction of only a slight error.

From the foregoing description and consideration, it? is now apparent that by using the same slide wireor adjustable resistance- W, and by introducing a shunt S, the temerature range of the scale of the instrument 1s varied or changed; and by changing the value of the fixed resistance R, the temperature ran e of the instrument may be shifted, thong keeping the extentof range the same.- Thus, introducin a shunt S may, as shown in Fi from 500 d egrees to 1,000 degrees to 500 degrees to 600 de rees; and by changing the 1% the range of the instru- 1,000 degrees to 300 degrees to 800 degrees.

It will, of course, be understood that R can be'changed or varied to shift the temperature range of the instrument without regard to whether S is present or not; and that irrespective of the valueof R or the posit-ion of the temperature range of the instrument, the shunt S may be used to changethe range of the instrument.

From the foregoingdescription, it follows a difl'erential galvanometer, or other differ- 1, change t e instrument range that I have devised an instrument involving zero :or balancing method, wherein a uni-- form scale is possible, the scales for any number of instruments being interchangeable; that I have provided means for both changing the range of the instrument, and? for shifting the temperature range of the:

instrument; and that I have provided a modified or compensated slide wire or vari-,

able resistance for insuring a uniform scale.

By my invention a plurality of instruments may be made up as standards and all similar to each other, and then by theuse'of the shunt S or by the chan e in the resistance of R, with interchangea le ther mometers T, suit such standard instrument for a variety of temperature ranges or a variety of positions of temperature range.

esaid clrcuit branches comprising a resistance And, furthermore, by the arrangement scribed, there is perfect compensation for the thermometer leads.

What I claim is:

.1. In an electrical measuring instrument,,

the combination with circuit branches, 'having an adjustable resistance common to said circuit branches, of a uniform scale associated with said adjustable resistance, and a resistance in shunt to saidadjustable re-' sistance for determining the range of said scale.

' 2. In an electrical measuring instrument,

the combination with circuit branches,havmg an ad ustable reslstanc'e common to said branches, of a resistance 1n a branch changing non-uniformly with respect to a quantity to be measured, and a uniform scale associated with said adjustable resistance, said adjustable resistance being made non-uniform in resistance with respect to its length for compensating for the non-uniform change in resistance of said branch resistance. 3. In an electrical measuring instrument, the combinationwith circuit branches, said branches closed through a common path, a slide wire common to said branches, a movable contact .en aging said slide wire and included in said common. path, said slide wire. made non-uniform in resistance with respect to its length for compensatin for a non-uniform change of resistance in a ranch changing non-uniformly with res ect to a quantity to be measured, and a uni orm scale associated with said slide wire.

4. In an electrical measuring instrumenti the combinationwith a slide wire, of circuits to be balanced thereby, said wire being nonuniform in resistance per unit of length for compensating for a non-uniform changeof tact, a winding of a difi'erential instrument and a variable resistance in one branch, the

r. Winding f. said instrument and a fixed resistance in another branch, acsource of current, and a un form scale associated resistance connected in one branch, another,

winding of said differential galvanometerand a fixed resistance connected in another branch, a source of current, anda uniform scale'associated with said movable contact.

7 In an electrical measuring instrument, circuit branches balancing means common to and a movable contact, a winding of a differential galvanometer and a variable resistance connected in one branch, another windin of. said difl'erential galvanometer and a xed resistance connected in another branch, said galvanometer windings being equalin resistance, a source of current, and a uniform scale associated with said movable contact. I H

8. In anelectricalmeasuring instrument, circuit or resistance balancing means, comprising a resistance and a movable contact,'a,

winding of a differential instrument and a thermometer resistance connectedm one branch, another winding of said differentialinstrument and a fixed resistance connected in another branch, a connection from said movable contact to a terminal of said ther-.

mometer resistance, said connection includ-v ing a source of energy, and a uniform scale associated with said movable contact.

9. In an electrlcal temperature measuring instrument, circuit or resistance balancing, means comprising a resistance and a movable contact, a wmdmg of a differential galvanometer and a thermometerresistance connected in one branch, another windin of said difi'erential galvanometer and a resistance connected in another branch, a source of current, I and a uniform scale associated with said movable contact. v

10. In an electrical temperature measuring instrument, circuit or resistance balancxed ing means comprising an adjustable resistance and a movable contact, a winding of a differential instrument and a thermometer resistance connected 1n one branch, another winding of said differential instrument and afixed resistance connectedin another branch, and a source of current, said ad ustable resistance; being non-uniform 1n I'GSlStflIlCG with respect to its length to compensate for disproportionate change of resistance with respect to temperature of the thermometer resistance, whereb associated with sand movable contact.

anniform scale may be o windin a fixef 11. In an electrical temperature measuring 1nstrument,.c1rcu1t or resistance balancing means comprising a resistance and a movable contact, a winding of a differential instrument and a thermometer resistance connected in one branch, another winding of said differential instrument and a fixed resistance connected in another branch, and a source of current, said fixed resistance being equal to the resistance of said thermometer corresponding with the lower end of the temperature range of the measuring instrument.

12. In an electrical temperature measuring instrument, circuit or resista'nce balancing means'comprismg a resistance and a movable contact, a winding of a differential instrument and a thermometer resistance connected in one branch, another winding of said differential instrument and a fixed resistance connected in another branch, a source of current, said fixed resistance being equal to the resistance of said thermometer corresponding with the lower end of the temperature range of the measuring instrument, and a uniform scale associated with said movable contact.

13. In an electrical temperature measur ing instrument, circuit or resistance balancing means comprising a winding of a differential instrument and a thermometer resistance connected in one branch, another of said differential instrument and resistance connected in another branch, and a source of current, said fixed resistance being equal to the resistance of .said thermometer at a temperature corresponding with the low end of the range of tie measuring instrument.

v 14. In an electrical temperature measuring instrument, circuit or resistance balancing means comprising a slide wire or ITSlStance and a movable contact, a winding of adifl'erential instrument and a thermometer resistance connected in one branch, another windin of said differential instrument and a: fixe resistance connected in another fbran'ch, and a source of current, said slide wire. "or resistance having a resistance at 1 least e ual to half of the resistance increment 0 said thermometer resistance.

15. In an electrical measuring instrument, circuit or resistance balancing means comprisin an adjustable resistance, a winding ofa iflerential instrument and a variable resistance connected in one branch, the other Windin of said differential instrumentand a fixe resistance connected in another branch, and a resistance in shunt to said adjustable resistance.

16. In an electrical measuring instru- -ment, circuit or resistance balancing means comprising an adjustable resistance with a movable contact, a winding of a differential instrument and .a variable resistance connected in one branch,-'the other winding of said differential instrument and a fixed resistance connected in another branch, a

resistance in shunt to said adjustable re-.

sistance, and a scale associated with said movable contact."

-17.' In an electricaltemperature measuring instrument, circuit or resistance balancing means comprising an adjustable resistance-with amovable contact, a winding of a differential instrument and a thermometer resistance connected in one branch, the other winding of said differential instrumentand -a fixed resistance connected in another branch, a source of current, and a resistance connected in shuntwith said adjustable resistance.

18, In an electrical temperature measuring instrument, circuit or resistance balancing means comprising an adjustable resistance with a movable contact, a winding of-a differential instrument and a thermometer resistance connected in one branch, the other windin of said differential instrumenfiand resistance connected in another branch, a source of current, a resistance con-' nected in shunt with said adjustable resistance, anda scale associated with said movable contact.

19. In an electrical temperature measuring instrument, circuit or resistance balancing means comprising an adjustable resistance with amovable contact, a w1nd1ng of a differential instrument and a thermometer re-..

sistance connected in one branch, the other winding of said differential instrument and a fixed resistance connected in another branch, and a source of current, said adjustable resistance' being modified to compensate for the disproportion ate change in resistance of said thermometer with respect to temperature, whereby a uniform scale may be associated with said movable contact.

20. In an electrical temperature measuring instrument, circuit or'resistance balancing means comprisinga resistance ad ustable by a movable contact, a winding of ,a differential instrument. and a thermometer lead and a thermometer resistance connected in a branch, another winding of said differential instrument anda fixed resistance and a second thermometer lead connected in another branch, and a connection from the thermometer end of said second thermometer lead to said movable contact.

21. In an electrical temperature mcasur ing instrument with perfect elimination of thermometer lead error, a resistance adjustable by a movable contact, a winding of a differential instrument a thermometer lead and a thermometer resistance connected in one branch, another wmdm ential lnstrumenti and a fixe resistance and of said differ- 35 therewith and connected in said, common a second thermometer lead connected in another branch, a connection from the thermometer end of said second thermometer cuit branches, of an adjustable balancing resistance, a thermometer reslstance, said adjustable resistafibe being made non-uniform in resisting with respect to its length for compensating for the noniuniform chan e in said thermometei resi'stance with respect to temperature, and auniform scale graduated'in temperature units associated with saidadj ustable resistance. 23. In an electrical tem witbranches, of an adjustable balancing resistance, a movable 'contactfor adjusting said resistance, [a thermometer resistance,

. branches, said branches bein said adjustable resistance being made nonuniform for compensating for the non-uniform change in resistance ofsaid thermometer resistance, equal increments of move ment of said movable contact corresponding with equal; increments. of temperature change.' v

24. In an electricaltemperaturemeasuring instrument, the combination with circuit closed through a common path, an adjustab e balancing resistance, a movable contact .cotiperating path, an associated thermometer resistance,

said adjustable resistancebeing made nonuniform for compensating for the non-uniform' change in resistance of said thermometer resistance, equal increments of movement of said movablev contact corresponding with equal increments of temperature change. f

25. In an' electrical temperature measuring instrument, the combination with circuit branches,- said clrcuit branches closed through V a'common path, an adjustable balancing re- .7 sistan'ce common to said branches,

a cooperatin-g movable contact in said common path, a thermometer resistance in one branch, windings of a diflerential instrument connected in different brancheS said adjustable balancing. resistance being made non-uniform for compensating for the non-uniform change in resistance of said thermometer resistance, equal increments of movement of said movable contact corresponding with equal increments of temperature change.

26; In an electrical temperature measur1-.v

ing instrument, the: combination with circuit branches, said' branches being closed through a common path, an-adjustable-balancing re-' sist'ance, a movable contact cooperating I rature measurqll'lg' instrument, the combinat on wlth cirv therewith and connected in said common path, anassociated thermometer resistance,

said adjustable resistancebeing made non-,

, adjustable V resistance.

27- In' an electrical temperature measuring instrument, the combination with circuit branches, said circuit through acommon path, an adjustable balancing resistance common to said branches, -a coiiperating movable contact in said cominon path, a thermometer resistance in one branch, windings of a differential instrusaid movable contact corresponding temperature branches closed ment connected in different branches, said adjustable balancing resistance being made non-uniform for compensating for the nonuniform change in resistance of'said ther mometer resistance, equal increments of movement of said movable contact corresponding with equal increments of temperature change, and a resistance in shunt to said adjustable resistance.

28. In an electrical measuring instrument, the combination with branches, having an adjustable resistance common to said circuitbranches, of windings of a differential instrument connected in the different circuit branches, and a resistance in shunt to said adjustable resistance for determining the range of the instrument.

29..In an electrical measuring instrument, the combination with circuit branches closed through a common path, of windings of a differential instrument connected in vthe difi'erent circuit branches, an adjustable 1 reslstance com on to said branches and en- \gaged by a ovable contact in said com- \monpath, a resistance in one branch sub- ,jected to and varied by the quantity to be measured, and a scale-associated with said adjustable resistance. I

i 30. In an electrical measuring instrument, the combination with circuit branches closed through a common path, of-windings of a differential instrument connected in the different circuit branches, a slide wire, a movable contact engaging said slide wire for dividing the same between said branches, a. resistance in one branch subjected to and ,varied by the quantity to be measured, and

a scale associated with said slide wire.

' 31. In an electrical measuring instrument, the combination with circuit branches closed through a common path, of windings of a differential instrument connected in the diflerent branches, a slide wire, a movance with respect to its length for compen 32. In an electrical measuring instrument, the combination with circuit branches, of a slide wire common to said branches, windings of a diflt'erential instrument connected,

in the different branches, and a resistance vconnected in one branch and subjected to resistance being Corrections Letters PatentN0. 950,513. I

v and varied by the quantity to be measured, the slide wire resistance being at least half the range in resistance of said resistance connected in one branche 33. In an electrical measuring instrument, the combination with circuit branches, of a slide wire common tosaid branches,windvmgs of a differential instrument connected in thedifi'erent branches, at variableqesistance connected in one branch, the slide wire at least half the range in resistance of said variable resistance, and a resistance in shunt to said slide wire.

34.' In an electricalmeasuring instrument, the combination with circuit branches, of a slide wire commonto said branches, windings ofa difi'erential instrument connected in the different branches, a resistance connected in one branch and subjected to and varied by the quantity to be measured, the slide wire resistance being at least half the range in resistance of said resistance coilnected in one'branch, and a scale associated with said slide wire.

35. In an electrical measuring instrument,

It is hereby certified that in Letters Patent No. 950,513, grantedMar'ch 1,1910, upon the application of EdwinF. Northrup, of Philadelphia, Pennsylvania, for an improvement Electrical Measuring Instruments, errors appear in the brinted' specification requiring correction as follows: Page 4, line 45', in the equation, the letter Z should read 1 (unity), page 5 lines 7 3 and 83, after the word branches commas should be inserted; page'7, line 13; the word resistingl should read raw'atcmqe; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record ofthe case inthe Patent Signed and sealed this 22d day of March, 1);, 1 10.

CL 0. s mmers,

Acting C'mnmisaioner of Patents.

ance with respect to its length for compen 32. In an electrical measuring instrument, the combination with circuit branches, of a slide wire common to said branches, windings of a diflt'erential instrument connected,

in the different branches, and a resistance vconnected in one branch and subjected to resistance being Corrections Letters PatentN0. 950,513. I

v and varied by the quantity to be measured, the slide wire resistance being at least half the range in resistance of said resistance connected in one branche 33. In an electrical measuring instrument, the combination with circuit branches, of a slide wire common tosaid branches,windvmgs of a differential instrument connected in thedifi'erent branches, at variableqesistance connected in one branch, the slide wire at least half the range in resistance of said variable resistance, and a resistance in shunt to said slide wire.

34.' In an electricalmeasuring instrument, the combination with circuit branches, of a slide wire commonto said branches, windings ofa difi'erential instrument connected in the different branches, a resistance connected in one branch and subjected to and varied by the quantity to be measured, the slide wire resistance being at least half the range in resistance of said resistance coilnected in one'branch, and a scale associated with said slide wire.

35. In an electrical measuring instrument,

It is hereby certified that in Letters Patent No. 950,513, grantedMar'ch 1,1910, upon the application of EdwinF. Northrup, of Philadelphia, Pennsylvania, for an improvement Electrical Measuring Instruments, errors appear in the brinted' specification requiring correction as follows: Page 4, line 45', in the equation, the letter Z should read 1 (unity), page 5 lines 7 3 and 83, after the word branches commas should be inserted; page'7, line 13; the word resistingl should read raw'atcmqe; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record ofthe case inthe Patent Signed and sealed this 22d day of March, 1);, 1 10.

CL 0. s mmers,

Acting C'mnmisaioner of Patents.

Corrections in Letters Patent No. 950

' It is hereby certified that in Letters Patent No. 950,513, granted March 1, 1910,

- upon the application of Edwin F. Northrup, of Philadelphia, Pennsylvania, for an improvement in Electrical Measuring Instruments, errors appear in the printed specification requiring correction as follows: Page 4, line 45, in the equation, the letter I. should read 1 (unity); page 5, lines 73 and 83, after the word branches commas should be inserted; page 7, line 13, the word resisting should read rcs/sflmc'e, and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Signed and sealed this 22d day of March, A. D., 1910.

[seam] C. C. BILLINGS,

Acting Commissioner of Patents. 

